This invention relates to gas turbine engines and, more particularly, to a passive bleed system for reducing drag on a gas turbine propulsion system.
Gas turbine engines are widely known and used for power generation and vehicle (e.g., aircraft) propulsion. There is a general trend to improve fuel efficiency of gas turbine engines. One technique for achieving better fuel efficiency is to reduce drag. For example, during flight, friction between airflow and the engine or other related components such as a nacelle produces drag that results in greater fuel consumption. Depending on a variety of different factors, the airflow can be laminar or turbulent. Laminar airflow generally produces less friction than turbulent airflow. Therefore, laminar airflow is desirable for reducing drag and improving fuel efficiency.
Presently, there are certain designs having an external shape that naturally produce laminar airflow over a certain portion of the nacelle. However, for these designs, the laminar airflow occurs under specific conditions, such as at cruise, and is subject to turbulent airflow under other conditions such as take-off and fan windmill conditions. Furthermore, debris carried within the airflow that has impacted and contaminated the smooth nacelle surface can cause a transition from laminar airflow to turbulent airflow. For example, insects that have impacted the nacelle leading edge can cause flow to transition from laminar to turbulent. Therefore, these nacelle designs are subject to the disadvantage of greater drag once the airflow changes to turbulent. Thus, there is a need for a system capable of controlling the airflow to change from turbulent airflow to laminar airflow.